Wood treating preparation



Patented May 19, 193G UNETED STATES 2,041,555v PATENT OFFICE WOOD TREATING PREPARATION Gilbert Gunn, Pollokshaws, Scotland, assig'nor to- Oelcure Corporation of America, Worcester, Mass., a corporation oi. Massachusetts No Drawing. Application November 16, 1934, Serial No. 753,308. In Great Britain November 4 Claims. (Cl. 134-785) This invention relates to wood treating preparations and has for one of its objects a dry preparation containing all the necessary ingredients for treating woodto preserve it from rot and attack by insects, except the water required to dissolve the ingredients at the time the wood is impregnated therewith.

Another object is to provide a preparation which contains a fireprooflng ingredient as well as preservative constituents.

Heretofore when wood preservative substances, like soluble dichromates and copper salts, have been used as wood preservatives they have been acidified by acetic acid in liquid form, usually in the form of pyroligneous acid, the function of which is by acidifying the mixture to intensify the oxidizing action ofthe dichromate on the ligncse and other constituents of the wood and to prevent the separation of substantially insoluble basic copper chromate before the wood has been impregnated.

Acetic acid, either in pure form or as pyroligneous acid, is a liquid and has a corrosive action on many materials. It is, therefore, troublesome and expensive to ship. The quantity of acetic acid required is not a large part of the total preparation, but the fact that acetic acid is a corrosive liquid necessitates either the separate shipment of the dichrom'ate and copper salt, on the one hand, and the acetic acid on the other or the use of liquid-tight non-corrosive containers for the mixture of all three ingredients.

According to the present invention, therefore, a dry acidifying material, is used so that all of the ingredients may be shipped in dry form, advantageously mixed so that all that is required is to add water and apply.

The acidifying material is a salt which, when a solution thereof is brought into contact with the wood, will yield an acid. Such salts are chromium or aluminum acetate or the formate, butyrate and many other salts of such metals.

The action of such material is apparently due to hydrolysis, followed by a progressive reaction between the basic part of the compound and the constituents of the wood which leaves behind the acid in a free state to intensify the oxidizing action of the dichromate and prevent premature separation of substantially insoluble basic copper chromate.

As the action or the dichromate part oi the preparation is to oxidize certain constituents of the wood, I prefer not to use salts of reducing acids, such as oxalic, tartaric or citric acids.

Further, for uses where corrosion of metal parts is to be avoided, it is preferable to use a hydrolyzable salt of a volatile acid like acetic acid instead of a solid, non-volatile acid, like malic or lactic acid. A volatile acid will evaporate after it has aided the action 01 the dichromate on the wood and not remain to act as a corrosive agent on iron, steel or other parts embedded in or in contact with the wood.

I have also found that salts of volatile relatively weak acids, like acetic acid, have marked advantages over volatile strong acids like hydrochloric acid. Likewise, salts of sulphuric and nitric acid are not as suitable as salts of acids of the acetic acid type.

The hydrolyzable salt may be formed from any m one of a number of metals forming very weak bases, like chromium, iron, copper and aluminv ium.

Various soluble dichromates may be used, although the cheapest and hence most advantageous ones are sodium and potassium dichromates. The former is highly deliquescen-t and has such a strong affinity for water that it will extract water of crystallization from copper sulphate crystals (CuSOa5I-Ir0) and go into solution in the water so extracted. The result is a paste, and, if the mixture contains chromium acetate, the latter will dissociate prematurely and give off acetic acid.

The production of a paste may be avoided by 25 using either potassium or ammonium dichromate, which is much less deliquescent, or partially or wholly dehydrated copper sulphate or some other soluble copper salt, like the chloride, which does not contain sumcient water of crystallization to permit the mixture to become pasty.

Small percentages of chemicals which increase toxicity but do not corrode metals may be added, for example: boric acid HaBOa: cadmium chloride CdClzZI-IzO and others.

A suitable formula for rny preparation in the dry state is the following:-

I Per cent Potassium dichromate (KzCraO'z) $8.15 Copper sulphate (CuSOsfil-IzO) 43.00 m Chromium acetate (C1(C2H3O2)3H2O) 4.55 Boric' acid (HzBOs) 4.30

0.93 or say 1 lb. of the above preparation per 45 U. S. gallon will give a solution (full strength) for brushing or spraying of the following composition:

Per cent The boric acid is not an essential constituent and may be omitted if desired. For the treatment of timber under pressure one half the foregoing perw centages in solution of the dichromate and cop-=- per sulphate may be used but it is advisable toretain the original percentagesof chromous acetate and boric acid.

I have found that wood which has been treated with a slightly acid aqueous solution of a soluble dichromate and a soluble copper salt is rendered substantially impenetrable to salt and other solutions. Hence wood so treated-cannot be sub- 1 sequently impregnated with solutions of fireprooiing substances. I have found thatim pregnation with certain of such substancescan take place if they are mixed with the dichromate mixture.

I have found however if 'flreproofing material is mixed with the dichromate mixture to penetrate the wood with the latter, the impregnation of the wood with the preserving agents is interfered with in the case of many of the well known flreproofing agents due toinsoluble precipitates.

I have found however that boric acid canbe used very satisfactorily in admixture with soluble dichromate and copper salts.

A suitable formula for my flreprooflngcompo sition is the following:

- Per cent Potassium dichromate (KzClzOv) 34 Copper sulphate (CUSO4.5H2O) 30. Chromium acetate (Cr(C:HsO2)a.H2O)-.. 6 Boric acid (H4303) 30 Full strength of solution is obtained byadding 1 lb. of the above dry mixture to each U. 8. gallon water.

The strength of the solution may be varied widely depending on the hardness and other qualities of the wood or the like.

It is advisable for many reasons to dissolve .the mixture in hot water. One reason is, that chromium acetate reacts with the constituents of wood very slowly in cold water. Another reason is that boric acid is only sparingly soluble in of the dry mixture to advantage between 2 and The boric acid content may vary widely according to the nature of the wood and the degree of flreprooflng desired. Usually the percentage of boric .acid should not be much below 5 or better 10% or the flreprooflng qualities will be seriously impaired. 02 course, if the solution is diluted to any great extent and it is desired to obtain the maximum possible flreprooflng, the proportion of boric acid may be increased correspondingly.

'Ihe proportion of acidifying material used may also be increased to advantage, with dilution of the solution as the action of the acid is weakened by its dilution, and'the weaker the solution of dichromate the more it needs acid stimulation.

In place of boric acid I may. use as a fireprocflng material phosphoric acid and/or a phosphate and 'sufiicient acidifying material to prevent the precipita'tion of insoluble copper (or chromium) phosphate prior to impregnation of the wood. After the wood has been impregnated, precipita tionofinsoluble phosphates takes place due to the volatilization of the acid. The insoluble phosphates left behind are fire-proofing materials and being insoluble are not leached out by rain, etc.

In view of the need of acid to prevent premature precipitation of copper phosphate an acid phosphate such as mono=ammonium phosphate (NH4H2PO4) may be used. However, as neither phosphoric acid nor sulphuric acid are volatile, it may be desirable to use the tri-rbasic phosphate ((NHOJPOsl and secure the desired acidity by the use of more acetic acid or other volatile acid than would otherwise be necessary. Other phosphates thanammonium, such as sodium, potassium or even copper or zinc may be used.

When other phosphates than copper are used it is advisable to use additional copper or zinc sulphate to react with the phosphate added and thus avoid upsetting the relationship between the dich'romate. and copper salt necessary for preserplace of boric acid, a suitable proportion is an I amount equal (by weight) to the boric acid in the ditional copper or zinc sulphate and chromium acetate.

The above proportions may be varied widely,

the chief requirement being that there should be sumcient acid to keep the phosphates in solution during the impregnation period.

If desired the composition may include both boric acid and/or borax as well as phosphate.

I may use ammonium sulphate in small quantity if found necessary, but as in large quantity it tends to keep wood treated therewith moist indefinitely, it is not ordinarily as suitable as either boric acid or phosphates.

What is claimed is:

1. A new wood preservative in dry form, comprising a soluble dichromate, a soluble copper salt and a non-reducing salt of a weak volatile aliphatic acid and a base capable of reacting with the wood to liberate the acid part of such salt, the proportion of the last named salt being less than either of the first two salts.

2. A new wood preservative in dry form, comprising as major constituents a soluble dichromate, a soluble copper salt and a tire-proofing material of the group consisting of boric acid, borates and phosphates, and as a minor constituent a non-reducing salt of a weak volatile aliphatic acid and a base capable of reacting with the wood to liberate the acid part of such salt.

3. A wood preservative as in claim 1, in which the non-reducing salt is a salt of a metal of the group consisting of chromium, iron, copper and aluminum.

4. A wood preservative as in claim 1, in which the non-reducing salt is one of the group consisting of chromium and aluminum acetates.

' GILBERT GUNN. 

